Good Going

"How many caves and fountains that no eye has yet seen lie with all their fine furniture deep down in the darkness, and how many shy wild creatures are at home beneath the grateful lights and shadows of the woods, rejoicing in their fullness of perfect life!"—John Muir

The creatures evacuating Devil’s Sinkhole swirl into the dusking Texas sky like, well, bats out of hell. Each evening from April through October, over a million Mexican free-tails drop from their roosts, where they’re huddled 400 to the square foot, to begin circling counterclockwise inside the cave. Creating air currents to launch themselves in a 60-foot-wide bat tornado, they surge from the hole, streaming into the night in search of food. Though each four-inch-long Mexican free-tail weighs only as much as two quarters, the whole colony can suck down 20 tons of moths, weevils, stinkbugs, and other insects in a single night, traveling up to 100 miles before returning at dawn.

The bats have arranged a time-share with cave swallows, several thousand of which keep the roosts warm while the bats are out all night.

Not to be outdone, the swallows make their evening entrance by dive-bombing into the cavern. But other cave dwellers never leave: A couple of species of pale, blind crustaceans, one of which exists nowhere else on Earth, live in the freshwater lakes around the edges of the sinkhole’s 350-foot-deep base. The dank cave floor swarms with flesh-eating dermestid beetles, which museums often employ to clean animal skeletons; should a maladroit bat fall into their midst, they’ll reduce it to bones in minutes.

Texas itself is cavernous, with at least 4,000 known caves and sinkholes (and over 100 million bats), but Devil’s Sinkhole is its largest single subterranean chamber. It was formed when the ceiling of a limestone pit collapsed, leaving a 40-by-60-foot opening into the huge void. The breakdown created a cone of debris, now slick with guano, rising 200 feet up from a floor the size of a football field. Texans proudly note that if the mini-mountain weren’t there, the sinkhole would be capacious enough to hold the state capitol. —Elisa Freeling